1. The large size of the rectenna, 8.5 x 11 km, will require a significant quantity of supporting structures to develop appropriate look angles and shapes. 2. Alignment and accuracy requirements are not expected to be critical. 3. Conventional construction materials are expected to be adequate. 4. Construction allowing accessibility for conventional long term maintenance and repair will be required. 5. No unusual thermal environments are expected to exist in and around the antenna. 8. 2. 2 RF-DC CONVERSION This subsystem, commonly called the rectenna, collects the RF energy and converts it to de. The power grid accumulates the power at a relatively low de voltage and distributes it to the de switch yard which centralizes and controls the flow of power to other subsystems, as explained in subsection 8. 3. This discussion will be limited to the collection and conversion of the RF energy and the characteristics of the safety zone. There are numerous variables that determine the overall size of the rectenna, including RF frequency, size of the transmit array, power taper on the transmit array, geographic location, fraction of the total beam interception, pointing accuracy of the antenna, and random phase error. These variables can be analyzed and evaluated for a given SPS design. Figure 8-2 represents the current status of these variables. The elliptical rectenna is 8.5 x 11 km and consists of approximately 13.6 billion conversion elements. A single element consists of a half-wave dipole, an integral low pass filter, a diode rectifier, and an RF bypass capacitor. The dipoles are de insulated from the ground plane and appear as RF absorbers in parallel to the incoming RF wave. Their de outputs are in a parallel and series combination to result in the desired output voltage and current levels. The RF ground distribution pattern (Fig. 8-3) produced by the current baseline antenna system allows determination of the size of the ground receiving site once the acceptable power density level is established. A lack of standards prevents the establishment of exact parameters on minimum RF density; however, the effect can be analyzed by arbitrarily selecting various minimum RF densities. For an RF density of 0. 01 mW/cm2, the safety zone
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